A QOI viewer for a format Windows has never heard of
QOI, the Quite OK Image format, appeared in 2021 as a lossless alternative to PNG that encodes and decodes many times faster with a far simpler design. The whole specification fits on one page, so it spread quickly through game engines, emulators, screenshot tools and hobby graphics code. What it did not get was support in Windows: File Explorer shows a generic icon, and Photos cannot open the file.
QOI Viewer is a dedicated QOI viewer that behaves like a normal picture app. Make it the default for .qoi files and they open on a double-click, with the rest of the folder one arrow key away.
Because QOI is lossless, the file you are holding is an exact copy of the pixels its creator saved. Converting it to PNG keeps that exactness; only JPG trades some of it for a smaller file.
Why you might have QOI files
If you did not choose QOI yourself, a program chose it for you. Some emulators and game tools save screenshots and texture dumps as .qoi because it is so cheap to write. Developers meet it while testing an encoder or shipping assets for an engine that loads QOI natively. And it occasionally turns up in downloads from people who simply like the format.
In every case the need is the same: see what the file holds, and get it into something the rest of your software accepts.
QOI to PNG, JPG or PDF in a few clicks
Open the image and click Convert on the command bar. PNG is selected first, since it is lossless like QOI and opens in every editor, browser and chat app. Pick JPG for a smaller photo-style file, TIFF for print work, PDF to attach to a document, or ICO to use a small graphic as a Windows icon (it is scaled to fit 256 pixels).
For a folder of screenshots, switch Convert to Whole folder. The run goes through every readable image beside the one you opened, without entering subfolders, shows its progress, and can be cancelled partway.
Looking closely at pixel graphics
A lot of QOI content is sprite sheets and small game art. Zoom reaches 3200%, the plus and minus keys step it, and 0 returns to actual size. Fitting never stretches a small image past its real size, and once you zoom past 100% pixels are drawn as hard-edged squares instead of being smoothed. Behind the photo in Settings sets the backdrop to Near black, Mid gray or White.
One thing to know if you are checking an encoder: what you see is a high-quality JPEG rendering of the file, so transparency is not shown and single-pixel colors can shift slightly. For a pixel-exact comparison, convert to PNG and inspect that copy.
